In Mexico, City the metropolitan index of air qulity refers to: ozone (O3), particulates smaller than 10 micrometers(PM10), particulates smaller than 2.5 (PM2.5), Sulfur dioxide (SO2), nitrogen dioxide (NO2) and carbon monoxide (CO). The environmental regulation( NADF-009-AIRE-2006) also includes the IMECA calculation refers to the general level of pollution. I send you a table with the maths